Publications

The production in industrial buildings can have a large impact on the indoor air quality. For example, in beer breweries several processes influence the indoor air quality to a large extent, such as the fermentation process, which is accompanied by a strong emission of CO2 gas. Employees working inside this kind of rooms can be exposed to high CO2 concentrations. This paper presents Computational Fluid Dynamics (CFD) simulations to analyze three different ventilation configurations for an enclosure in which a fermentation process results in high CO2 emission levels. High-resolution steady 3D Reynolds-averaged Navier-Stokes (RANS) simulations were used to assess different ventilation methods and system designs, with the aim to realize a healthy indoor environment using a minimal amount of energy. The results showed that the ventilation configuration should be designed in such a way that it optimally takes advantage of the density difference between the ambient air and the released CO2 gas. In this particular case, a highly uniform downward directed flow using a low supply velocity showed the best performance (lowest CO2 concentrations), with a similar supply volume flow rate as used for the other configurations (and thus equal energy use).

Ventilation is of primary importance for the creation of healthy and comfortable indoor environments and it has a significant impact on the building energy heating and cooling demand. The aim of this study is to assess the application of time-periodic supply velocities to enhance mixing in mixing ventilation cases to reduce heating and cooling energy demands. This paper presents computational fluid dynamics (CFD) simulations of a generic mixing ventilation case, in which the time-averaged velocities and pollutant concentrations from a reference case with constant supply velocities were compared with those obtained from a case with time-periodic supply velocities (sine function). The unsteady Reynolds-averaged Navier-Stokes (URANS) CFD simulations indicate that the use of time-periodic supply velocities can reduce high pollutant concentrations in stagnant regions, reduces the overall time-averaged pollutant concentrations and increases contaminant removal effectiveness with about 20%. The influence of the period of the sine function was assessed and the results showed that for the periods tested, the differences are negligible. Finally, the URANS approach was compared with the large eddy simulations (LES) approach, indicating that URANS leads to very similar results (NMSE < 3.2%) as LES and can thus be regarded as a suitable approach for this study.

Airfoil shape can significantly influence the aerodynamic performance of vertical axis wind turbines (VAWTs). However, while the symmetric NACA airfoil series are widely used for VAWTs, the effect of parameters, which define the shape of an airfoil, on the aerodynamic performance of VAWTs has not yet been extensively studied. The current study, therefore, intends to systematically investigate the effect of airfoil maximum thickness tm on the aerodynamic performance of VAWTs for different tip speed ratios (λ). Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculations are performed on high-resolution gird. The results show that the optimum tm decreases from 24%c (airfoil chord) to 12%c when λ increases from 2.5 to 5.5. As higher λ corresponds to lower variations of angle of attack (α) of the blades, the better performance of thinner airfoils at such λ is associated to their higher Cl/Cd at such α. Higher stall angle could explain the higher CP of thicker airfoils at low λ. The current findings could support the optimization of airfoils for VAWTs.

Accurate and reliable CFD simulation of temperature stratification in indoor environment is needed for the design and evaluation of displacement ventilation in buildings. This paper presents a detailed and systematic evaluation of the capability of 3D steady RANS CFD simulations to predict the temperature stratification in a room. The evaluation is based on sensitivity analysis and validation with full-scale measurements of indoor air temperature. The results show that steady RANS can accurately predict the temperature stratification in an indoor environment. The SST k-ω model shows a better performance compared with other considered turbulence models.

Simplified methods to predict the flow between vertical plates cannot be applied to predict the flow patterns in active facades. Due to the presence of blinds and asymmetric inlet or outlet openings and heat transfer through the glazed surfaces (e.g. sun radiation), the flow is much more complex. This research provides an onset for a model that is capable of predicting the airflow in the cavity of an active facade (without any heat transfer). Therefore measurements and simulations are performed. The airflow is measured with two-dimensional Particle Image Velocimetry (PIV) and one-dimensional hot-film anemometry (HFA) under isothermal conditions. The measurements show some distinct flow features and low-frequency large-scale instationary behaviour and illustrate that the boundary conditions (e.g. dimensions of the inlet) have a major influence on the flow pattern in the facade. The results of Computational Fluid Dynamics (CFD) simulations are compared with the experimental results. It is shown that the two-dimensional CFD model is capable of predicting the general tendencies of the flow. The measurements suggest that the airflow in the facade is three-dimensional, which could not be confirmed by the steady three-dimensional simulations performed in this study.

Conventional ventilation methods often supply fresh air to the room with a steady supply flow rate, which might induce stagnant recirculation cells and stagnation zones that are characterized by high concentrations of contaminants. This paper presents computational fluid dynamics (CFD) simulations of isothermal mixing ventilation with a transient supply flow rate in a generic room. The time-periodic supply flow rate is described by a sine function with different amplitudes. It is shown that time-periodic forcing triggers the stagnant recirculation cells to continuously shift throughout the room, thereby reducing average (passive gaseous) concentration levels in the occupied zone volume compared to the steady supply of fresh air. The concentrations are lower when larger amplitudes are applied. The analysis indicates a reduction in contaminant concentration by up to 24% and an increase of the contaminant removal effectiveness by 24% for time-periodic supply conditions compared to steady supply, which offers new perspectives on healthy and sustainable ventilation for, among others, residential buildings, office rooms, ship cabins, train cabins and cars.

To investigate the validity of the traditional approach to implement wind-driven rain (WDR) in hygrothermal building envelope models, under real atmospheric conditions, a new set-up was developed at a test building. Reference wind speed and direction, WDR intensity, outdoor air temperature and relative humidity and the resulting moisture response of the wall to these environmental conditions (both hygroscopic loading and WDR) were simultaneously measured. The whole measurement data set was used for validation. Large differences between the measurement and simulation results were found and possible causes discussed. It is concluded that many influencing parameters interact, and that therefore precisely predicting the hygrothermal response of walls to wind-driven rain is very difficult.